We have a Potterton Puma 80E and until recently it has been working fine. The problem is that we have hot water on demand but it is over riding the heating so the heating won't come on?! Even when the shower is fully switched off it still drips hot water and is contsantly calling for hot water.
you must get the shower fixed as the boiler thinks that you want hot water all the time so the dhw flow switch in side of the boiler is made all the time stoping the diverter switching tom heating mode